ul a _design of colours_. Moreover, this design is only unfolded
when the tail is erected, and the tail is not erected in battle (as Mr.
Wallace's theory of the erectile function in feathers would require),
but in courtship; obviously, therefore, the purpose of the pattern, so
to speak, is correlated with the act of courtship--it being only then,
in fact, that the general purpose of the whole structure, as well as the
more special purpose of the pattern, becomes revealed. Lastly, the fact
of this whole structure being so large, entailing not only a great
amount of physiological material in its production, but also of
physiological energy in carrying about such a weight, as well as of
increased danger from impeding locomotion and inviting capture--all this
is obviously incompatible with the supposition of the peacock's tail
having been produced by natural selection. And such a case does not
stand alone. There are multitudes of other instances of ornamental
structures imposing a drain upon the vital energies of their possessors,
without conferring any compensating benefit from a utilitarian point of
view. Now, in all these cases, without any exception, such structures
are ornamental structures which present a plain and obvious reference to
the relationship of the sexes. Therefore it becomes almost impossible to
doubt--first, that they exist for the sake of ornament; and next, that
the ornament exists on account of that relationship. If such structures
were due merely to a superabundance of energy, as Mr. Wallace supposes,
not only ought they to have been kept down by the economizing influence
of natural selection; but we can see no reason, either why they should
be so highly ornamental on the one hand, or so exclusively related to
the sexual relationship on the other.

[48] Note C.

Finally, we must take notice of the fact that where peculiar
_structures_ are concerned for purposes of display in courtship, the
_elaboration_ of these structures is often no less remarkable than that
of patterns where colours are thus concerned. Take, for example, the
case of the Bell-bird, which I select from an innumerable number of
instances that might be mentioned because, while giving a verbal
description of this animal, Darwin does not supply a pictorial
representation thereof. The bird, which lives in South America, has a
very loud and peculiar call, that can be heard at a distance of two or
three miles. The female is dusky-green